*{
    margin:0px;
    padding:0px;
}
.top{
    width:100%;
    height:50px;
    background-color: black;
}
.top_content{
    width:75%;
    height:50px;
    margin:0px auto;/*上下边距、左右边距*/
    background-color: greenyellow;
}
.body{
    margin:20px auto;
    width:75%;
    height:1500px;
    background-color: cornflowerblue;
}
.body_img{
    width:100%;
    height:400px;
    background-color: sandybrown;
}
.body_content{
    width:100%;
    height:1100px;
    background-color: aquamarine;
}
.body_notice{
    width:100%;
    height:50px;
    background-color: aqua;
}
.footing{
    width:75%;
    height:400px;
    background-color: lightslategrey;
    margin:0px auto;/*若不设置，则会居左*/
}
.footing_content{
    weight:100%;
    height:330px;
    background-color: darkslategrey;
}
.footing_subnav{
    width:100%;
    height:70px;
    background-color: black;
}